System and method for providing a handoff leg associated with a preexisting leg in a network environment

ABSTRACT

A method for facilitating communications between wireless networks is provided that includes communicating with a mobile station and transferring a communication session from a first wireless link to a second wireless link. The mobile station is operable to negotiate a first wireless link with a first wireless network, to establish a communication session with a device using the first wireless link, and to facilitate a session handoff with a second wireless link with the second wireless network using the second wireless interface. The handoff is enabled by associating the first wireless link to the second wireless link.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to network communications, and,more particularly, to a system and a method for providing a handoff legassociated with a preexisting leg in a network environment.

BACKGROUND OF THE INVENTION

Networking architectures have grown increasingly complex incommunications environments. In addition, the augmentation of clients orend users wishing to communicate in various network environments hascaused many networking configurations and systems to respond by addingelements to accommodate the increase in networking traffic and thevarious enhancements that have been provided by numerous communicativeplatforms. In recent years, a series of protocols and architectures havebeen developed in order to accommodate a diverse group of end usershaving various needs. Some of these protocols relate to issuesassociated with handoffs (sometimes referred to as handovers).

As both public and private network systems grow in size and insophistication, proper routing and efficient management of communicationsessions and data flows becomes even more critical. In cases whereprotocols are unable to accommodate a given flow, an end user isprecluded from enjoying the benefits of a given communicationarchitecture. Advances in technology have resulted in the deployment ofvarious types of wireless networks. However, while most of thesewireless networks often provide service to adjacent and/or overlappingphysical spaces, most cellular and enterprise network protocols areincompatible. Accordingly, the ability to provide an effective mechanismto properly process, handoff, and direct communications for an end userseeking to realize the benefits provided by multiple networkenvironments offers a significant challenge to network operators,component manufacturers, and system designers.

SUMMARY OF THE INVENTION

In accordance with the present invention, techniques for supportinghandoff between cellular and enterprise wireless networks are provided.According to some embodiments, these techniques enable a mobile stationto maintain a communication session that is handed between cellular andenterprise wireless networks. In particular, these techniques can enablea mobile station, alone or in combination with a mobility application,to produce a handoff leg association with a pre-existing call leg.

According to a particular embodiment, a method for facilitatingcommunications between wireless networks is provided that includescommunicating with a mobile station and transferring a communicationsession from a first wireless link to a second wireless link. The mobilestation is operable to negotiate a first wireless link with a firstwireless network, to establish a communication session with a deviceusing the first wireless link, and to facilitate a session handoff witha second wireless link with the second wireless network using the secondwireless interface. The handoff is enabled by associating the firstwireless link to the second wireless link.

More particular embodiments of the present invention include the use ofone or more of the following: a unique session ID, a unique handoffnumber, caller ID or automatic number identification values, and dualtone multi-frequency (DTMF) codes. These items may be used to provide aneffective association between two call legs (e.g. a cellular call and avoice over IP (VoIP) call). In addition, certain operations performed bya mobility application unit or device may also be associated withauthentication procedures, whereby auth-codes are exchanged with anassociated mobile station.

Embodiments of the invention provide various technical advantages. Forexample, one or more of the techniques may provide for an effectivehandoff to allow a mobile station to roam between cellular andenterprise wireless networks. According to some embodiments, thesetechniques may reduce cost and increase performance by empowering themobile station to select between available networks. Furthermore, byutilizing both cellular and enterprise networks, a mobile station mayincrease its range of use. In addition, handoff between cellular andenterprise networks may be provided with little or no change to serviceprovider networks and/or enterprise networks. Also, these techniques maybe used without modification of signal protocols and without dependenceupon any existing signal protocol. Furthermore, using the disclosedtechniques, trust boundaries between service providers and enterprisesmay be preserved.

Other technical advantages of the present invention will be readilyapparent to one skilled in the art from the following figures,descriptions, and claims. Moreover, while specific advantages have beenenumerated above, various embodiments may include all, some, or none ofthe enumerated advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and itsadvantages, reference is now made to the following description, taken inconjunction with the accompanying drawings, in which:

FIG. 1 illustrates a communication system having elements that supporthandoff between cellular and enterprise wireless networks;

FIG. 2 is a block diagram illustrating functional components of amobility application from the communication system;

FIG. 3 is a block diagram illustrating functional components of a mobilestation from the communication system; and

FIG. 4 is a flowchart illustrating several methods for effecting handoffbetween cellular and enterprise wireless networks.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a simplified block diagram that illustrates a communicationsystem, indicated generally at 10, for executing an effective handoffbetween two call legs, which may exist in a network environment. Inaddition, communication system 10 provides various techniques forassociating related call legs. Some of these operations may relate tofeature-based handoffs, (e.g. park/transfer/etc.), while others mayrelate to make-before-break scenarios that do not necessarily use anyfeature for handoff. In make-before-break scenarios, a new call (orcall) is made (successfully) before the old call (or leg) is torn down.

Communication system 10 comprises a cellular network 12 and anenterprise network 14 interconnected through public switched telephonenetwork (PSTN) 16. One or more base stations 18 couple to cellularnetwork 12, and one or more access points 20 couple to enterprisenetwork 14. Enterprise network 14 includes a gateway 22, a call manager24, and a mobility application 26. System 10 also includes mobilestation 28. In general, mobile station 28 may communicate with a remotedevice through cellular network 12 using base station 18 and/or throughenterprise network 14 using access point 20. The elements of system 10can operate to permit mobile station 28 to maintain a communicationsession that is handed between cellular network 12 and enterprisenetwork 14. According to particular embodiments, mobility application 26and/or mobile station 28 utilize one or more of various private branchexchange (PBX) functions to effect handoff between cellular network 12and enterprise network 14.

Communication system 10 executes an effective and a superlative handoff,whereby the call is anchored in enterprise network 14 (e.g. via mobilityapplication 26). When a call is placed, the call lands on mobilityapplication 26, which recognizes, and is aware of, the call. Hence, whenmobile station 28 moves to cellular network 12, mobility application 26receives a “silent call” from mobile station 28 and, in response to thesilent call, mobility application 26 collaborates with call manager 24to switch (or to transfer [on the fly]) the call. In a similar,reciprocal fashion, when mobile station 28 moves back to enterprisenetwork 14 it communicates with mobility application 26, which transfersthe call from a cellular call leg to a voice over IP (VoIP) call leg.

The transfer can be executed in several ways, but the net effect of thetransfer is that a real-time protocol (RTP) stream remains constant suchthat voice traffic can be understood. The RTP stream is essentiallyswitched back and forth from a voice gateway and the VoIP handsetplatform. One problem associated with this operation is that when a callis made to mobility application 26 (which is generally anchoring thecall), mobility application 26 needs to coordinate or associate multiplecall legs (i.e. match a VoIP call to a cellular call). The situation canbe even more challenging when mobile station 28 is roaming.

In accordance with the teachings of the present invention, communicationsystem 10 addresses these issues and others in the following manner.Mobility application 26 provides handoff services for multiple calls tomultiple dual mode phones (e.g. mobile station 28). When mobilityapplication 26 receives a handoff-call via cellular network 12, it needsto identify the particular dual-mode phone and to recognize the activecall in order to perform the handoff.

Several methods are provided herein to achieve this goal. (Note thateach of these methods is detailed below with reference to FIG. 4,however a brief discussion is offered here in order to provide anoverview of these processes).

The first process is associated with a unique handoff-number. In thefirst process, mobility application 26 maintains a pool of E.164 DNs andit can assign a unique handoff-DN. Thus, mobility application 26 canselect one number from the pool of numbers and assign this DN to thedual-mode phone: either for the duration of the call or for a durationof a handoff transaction. On receiving the handoff-call, mobilityapplication 26 uses the handoff-DN (on which it received the call) tolookup the ongoing active call for handoff. For example, the dual-modephone may send a handoff-request message with the call ID of the activecall, whereby mobility application 26 selects a unique handoff-DN andreturns it to the phone in the handoff-response.

Mobility application 26 maintains the binding between the handoff-DN andthe call-ID of the active call from the dual-mode. Mobile station 28(i.e. the dual-mode phone) places a call to the handoff-DN. When thiscall is received by mobility application 26, it looks up the bindingbetween the DN on which it received the call and the call-ID todetermine the active call for the handoff.

The second process is associated with a unique session-ID and the secondprocess implements use of SMS or any of the signaling channel (e.g. useof dual tone multi-frequency (DTMF) codes). In this method, mobilityapplication 26 may assign the same handoff-DN to more than one mobilestation. A unique session-ID is used to identify the dual-mode phone andthe ongoing active call for the handoff. The session-ID may be agreedupon earlier, for example, during call-setup. Mobility application 26maintains a binding between the session-ID and the active call. Mobilestation 28 may use DTMF to signal the session-ID to mobility application26 when it is in cellular network 12. For example, for a wireless localarea network (WLAN) cell handoff, mobile station 28 makes a cell call tothe handoff-number and then dials the session-ID using DTMF. Mobilityapplication 26 uses the detected session-ID to bind the handoff call tothe ongoing active call. When mobile station 28 initiates or receives acall when it is in cellular network 12, it may generate the session-ID,and transmit it to mobility application 26 using DTMF.

The third process is related to a caller-ID/calling line identification(CLI)/automatic number identification (ANI) scenario. In this process,mobility application 26 may issue the same handoff-DN to more than onedual-mode phone (e.g. mobile station 28) and, further, use the caller-IDof the dual-mode phone (cell-number) to identify the ongoing active callto handoff. Mobility application 26 maintains a binding between thedual-mode phones cellular-DN and the active call from that dual-modephone. When the call comes in to a handoff-DN at mobility application26, it uses the caller-ID to determine the active call for handoff.

In an alternative embodiment, an authentication procedure may also beexecuted. In this scenario, the process is used to authenticate ahandoff call to the handoff-DN with any of the above associationmethods. The dual-mode phone and mobility application 26 can use anauth-code for authentication. The auth-code may be staticallyconfigured, or it may be agreed upon by mobility application 26 andmobile station 28 dynamically (e.g. during handoff signaling at callset-up). The dual-mode phone, after making the handoff-call, dials theauth-code using DTMF and mobility application 26 uses the detectedauth-code to authenticate the phone. This method could be used toprevent erroneous or malicious calls to a handoff-DN from triggering a“takeover” handoff of an active call. Note also that any combination ofthe above methods can be used.

Cellular network 12 represents communications equipment, includinghardware and any appropriate controlling logic, for providing wirelesstelephony services using cellular protocols and technology. Variouscellular protocols and technologies may be used by cellular network 12,including but not limited to global system for mobile communications(GSM), time division multiple access (TDMA), code division multipleaccess (CDMA), and any other appropriate analog or digital cellularprotocol or technology. Furthermore, cellular network 12 may utilizesignaling system 7 (SS7) protocol for signaling purposes. Cellularnetwork 12 may include any number of base stations 18, as well as basestation controllers, mobile switching centers, and other appropriatecommunications equipment for use in communicating with mobile station 28and PSTN 16. Thus, as illustrated, cellular network 12 may couple tobase station 18 to receive and transmit wireless signals to and frommobile station 28.

Enterprise network 14 represents communications equipment, includinghardware and any appropriate controlling logic, for interconnectingelements coupled to enterprise network 14. Thus, enterprise network 14may represent a local area network (LAN), a wide area network (WAN),and/or any other appropriate form of network. Furthermore, elementswithin enterprise network 14 may utilize circuit-switched and/orpacket-based communication protocols to provide for wireline telephonyservices. For example, elements within enterprise network 14 may utilizeInternet Protocol (IP). In addition, elements within enterprise network14 may utilize wireless standards such as the 802.11 family of wirelessstandards to provide for wireless telephony services. Note that the802.11 family of wireless standards includes, among others, 802.11a,802.11b, and 802.11g. Enterprise network 14 may also utilize interactivevoice response (IVR). Enterprise network 14 may include any number ofwireless network devices 20, gateways 22, call managers 24, and otherappropriate communications equipment for use in communicating withmobile station 28 and PSTN 16. In the embodiment illustrated, enterprisenetwork 14 includes access point 20, gateway 22, call manager 24, andmobility application 26. Access point 20 represents communicationsequipment, including hardware and any appropriate controlling logic, forproviding wireless access to enterprise network 14. Access point 20 mayutilize one or more of the 802.11 standards. However, any appropriatewireless standard or protocol may be used.

Note that both cellular network 12 and enterprise network 14 represent aseries of points or nodes of interconnected communication paths forreceiving and transmitting packets of information that propagate to orfrom an end user or mobile station 28. A subscription or an agreementmay be provided by either of the networks to offer cellular service toan end user of mobile station 28. Both networks offer a communicativeinterface between mobile station 28 and any suitable location within orexternal to communication system 10 and, thus, may be representative ofa GPRS service provider or any suitable LAN, WLAN, metropolitan areanetwork (MAN), WAN, virtual private network (VPN), or any otherappropriate architecture or system that facilitates communications in anetwork environment. Each network may implement a user datagram protocol(UDP)/Internet protocol (UDP/IP) communication language protocol in aparticular embodiment of the present invention. Communication system 10may utilize any form of transmission control protocol (TCP)/IP, oralternatively implement any other suitable communications protocol fortransmitting and receiving data or information within communicationsystem 10.

Gateway 22 represents communications equipment, including hardware andany appropriate controlling logic, for interconnecting enterprisenetwork 14 with cellular network 12 and/or PSTN 16. Gateway 22 may beused to convert communications between different communicationprotocols. For example, gateway 22 may convert communications receivedfrom cellular network 12 in SS7 protocol to any of various otherprotocols that may be used by enterprise network 14, such as protocolsassociated with the an integrated services digital network (ISDN)standard in the case of circuit-switched trunking and H.323, sessioninitiation protocol (SIP), or other appropriate protocols in the case ofIP-based trunking.

Call manager 24 represents communications equipment, including hardwareand any appropriate controlling logic, for providing telephony servicesover enterprise network 14. For example, call manager 24 may supportvoice over IP (VoIP) communications, using any of various protocols suchas SIP, signaling connection control point (SCCP) protocol, mediagateway control protocol (MGCP), H.323, and/or any other appropriateprotocol for VoIP. Furthermore, call manager 24 may act as an IP PBX andsupport PBX functions, such as hold, park, transfer, redirect, and/orother high level and low level call management features.

Mobility application 26 represents a server in one embodiment of thepresent invention, but alternatively could be replaced with any otherappropriate device (e.g. a router, switch, bridge, gateway, etc.) thatfacilitates the operations detailed herein. Mobility application 26includes any suitable collection of hardware, software, and controllinglogic to support handoff between cellular network 12 and enterprisenetwork 14. For example, mobility application 26 may, when appropriate,utilize PBX features to effect handoff of a communication sessionbetween cellular network 12 and enterprise network 14.

It should also be noted that the internal structure of mobilityapplication 26 and mobile station 28 are malleable and can be readilychanged, modified, rearranged, or reconfigured in order to achieve theirintended operations as they pertain to the handoff function outlinedherein in this document. As identified supra, software and/or hardwaremay reside in these elements in order to achieve the teachings of theleg association features of the present invention. However, due to theirflexibility, these elements may alternatively be equipped with (orinclude) any suitable component, device, application specific integratedcircuit (ASIC), processor, microprocessor, algorithm, read-only memory(ROM) element, random access memory (RAM) element, erasable programmableROM (EPROM), electrically erasable programmable ROM (EEPROM),field-programmable gate array (FPGA), or any other suitable element orobject that is operable to facilitate the operations thereof.Considerable flexibility is provided by the structures of mobilityapplication 26 and mobile station 28 in the context of communicationsystem 10 and, accordingly, they should be construed as such.

Note also that any number of additional functions (other than the callassociation operation detailed herein) may be provided by mobilityapplication 26. For example, one functionality provided by mobilityapplication 26 is to keep track of a feature state (e.g. hold, transfer,conference, etc.). Mobility application 26 may also translate betweenDTMF feature-codes and IP-PBX VoIP feature invocation, as appropriate.(Note that DTMF represents the system used by touch-tone telephones.DTMF assigns a specific frequency (consisting of two separate tones) toeach key so that it can easily be identified by a microprocessor.) Thiswould enable IP-PBX features (e.g. hold, caller ID, display functions,redirect, three-way calling, barge, web browsing, etc.) to be providedto mobile station 28 when the dual-mode phone is in cell network 12:even when there is no simultaneous data path. These operations alsooffer feature transparency across handoff scenarios. One operation ofcommunication system 10 is to have the feature-invocation from thedual-mode phone. This could be provided by communicating directly withmobility application 26 and, then, having mobility application 26 invokethe feature on the call-leg between mobility application 26 and theIP-PBX/far-end. When the dual-mode phone (e.g. mobile station 28) movesto cell network 12, it invokes features by dialing or initiating thecorresponding DTMF codes. Mobility application 26 then maps the codes tothe appropriate VoIP feature invocation signaling, and then continues toinvoke them on the call-leg between itself and the IP-PBX/far-end.

In operation of an example embodiment, when mobile station 28 goes tocellular network 12, there is a functionality in mobility application 26that invokes features on the end user's behalf. From an architectureperspective, when mobile station 28 is in enterprise network 14 it canrepresent itself in such endeavors. However, once mobile station 28moves to cellular network 12, it can no longer participate in suchsignaling. Thus, some device or element should offer a phone featureproxy function for mobile station 28 (for the purpose of invoking thefeature), as well as for the other participant (called party or callingparty). Without such a proxy feature, mobile station 28 becomes a “dumbdevice” that cannot take full advantage of a number of networkcapabilities. This phone feature proxy, as well as the leg associationfeature outlined herein, can reside in mobility application 26 (and/ormobile station 28) or in any other suitable location or element, whereappropriate and based on particular needs.

PSTN 16 represents communications equipment, including hardware and anyappropriate controlling logic, through which cellular network 12 andenterprise network 14 may communicate. PSTN 16 may include switches,wireline and wireless communication devices, and any other appropriateequipment for interconnecting cellular network 12 and enterprise network14. PSTN 16 may include portions of public and private networksproviding network transport services between various geographic areasand networks.

Mobile station 28 represents a mobile device, including hardware and anyappropriate controlling logic, capable of communicating with remotedevices through cellular network 12 and enterprise network 14 andmaintaining communication sessions with remote devices during handoffbetween cellular network 12 and enterprise network 14. Mobile station 28may communicate through cellular network 12 using base station 18 andthrough enterprise network 14 using access point 20. Furthermore, mobilestation 28 may interact with call manager 24 and/or mobility application26 when appropriate to utilize PBX features to effect handoff betweencellular network 12 and enterprise network 14.

In operation, mobile station 28 may initiate and receive telephone callsthrough cellular network 12 and/or enterprise network 14 to establishcommunication sessions with remote devices. Note that, as used herein, aremote device refers to any communications device capable ofestablishing communications sessions with mobile station 28, such asdevices located in cellular network 12, enterprise network 14, PSTN 16,or other linked networks. Furthermore, as used herein, a communicationsession refers to the transfer of voice, video, data, and/or otherinformation between two or more communication devices. For example,according to particular embodiments a communication session may involvea call between two communication devices or a conference call involvingtwo or more communication devices.

When mobile station 28 is in an area serviced by cellular network 12and/or enterprise network 14, callers who dial a telephone number orother appropriate identifier of mobile station 28 may initiate acommunication session with mobile station 28 through an appropriatenetwork. Similarly, mobile station 28 may dial a telephone number orother appropriate identifier of a remote device and initiate acommunication session with the remote device through an appropriatenetwork. Thus, mobile station 28 may function in two modessimultaneously or separately. For example, when in an area serviced byaccess point 20, mobile station 28 may act as an 802.11 wirelesstelephony device. When in an area serviced by base station 18, mobilestation 28 may act as a cellular phone. These areas may or may notoverlap.

Given the capability of mobile station 28 to place and receive callsthrough at least two networks, this presents at least four scenarios forinitiation of a communication session. In a first scenario, mobilestation 28 initiates a communication session by placing a call throughenterprise 14 using a wireless link with access point 20. In a secondscenario, mobile station 28 initiates a communication session throughcellular network 12 using a wireless link with base station 18. Notethat in either scenario, mobile station 28 may couple to a single remotedevice or to a conference call involving multiple remote devices. In athird scenario, a remote device initiates a communication session withmobile station 28, where mobile station 28 receives signaling and datathrough cellular network 12 using base station 18. In a fourth scenario,a remote device initiates a communication session with mobile station28, where mobile station 28 receives signaling and data throughenterprise network 14 using access point 20. Again, the communicationsession may be associated with a single remote device or with aconference call, and the remote device or devices may be located incellular network 12 and/or enterprise network 14.

At any point in time, mobile station 28 may determine to handoff acommunication session from cellular network 12 to enterprise network 14or from enterprise network 14 to cellular network 12. For example, afterestablishing a communication session, mobile station 28 may lose orbegin to lose connectivity with base station 18 or access point 20.Signal degradation may occur due to various causes. For example, mobilestation 28 may begin to lose wireless connectivity due to physicalmovement. When possible, mobile station 28 may switch between using basestation 18 and access point 20 for communications. Moreover, in certaincircumstances mobile station 28 may maintain a communication sessionduring handoff between cellular network 12 and enterprise network 14.

Handoff may occur when mobile station 28 travels from an area servicedby cellular network 12 to an area serviced by enterprise network 14.Handoff may also occur in the opposite direction, when mobile station 28travels from an area serviced by enterprise network 14 to an areaserviced by cellular network 12. However, handoff may occur at any otherappropriate time. For example, handoff may occur when mobile station 28is located in an area serviced by both network types due to apredetermined preference of one type of network, due to a spontaneouschoice of a user of mobile station 28, or in response to analyzing errorrates or other data associated with signaling provided by one or bothtypes of networks. For example, error rates may be associated withsignal strengths of base station 18 and access point 20, and may bedependent upon a location of mobile station 28.

In general, mobile station 28 and/or mobility application 26 may utilizePBX features such as hold, park, transfer, redirect, and other highlevel and low level PBX functions to provide for handoff betweencellular network 12 and enterprise network 14. Mobile station 28 maycouple to call manager 24 or mobility application 26 through parallelcall legs through two networks. The PBX feature may be used to terminateuse of an old call leg and initiate use of a new call leg to effecthandoff of a communication session from the old call leg to the new callleg.

One PBX feature that may be used to effect handoff is the park feature.The park feature may be provided in two forms, undirected park anddirected park. In undirected park, when a communication session isparked, a serving system such as call manager 24 may dynamically assigna park number associated with the parked communication session andreport the park number to the entity parking the communication session.In directed park, the entity parking the communication session mayselect a park number to be associated with the communication session tobe parked. To utilize directed park, the entity parking thecommunication session may monitor a set of park numbers to determine anavailable park number to prevent simultaneous use of any of the parknumbers. Both park variants may be utilized to support handoff ofcommunication sessions.

Consider mobile station 28 having a call established through accesspoint 20 and enterprise network 14 to a remote device. Any of the fourembodiments discussed above or a combination or modification of theembodiments may be used to effect handoff of the call. The call includesat least two call legs, a first leg between mobile station 28 andenterprise network 14, and a second leg between enterprise network 14and the remote device. Mobile station 28 may determine to utilizecellular network 12. For example, when exiting an area serviced byaccess point 20, mobile station 28 may detect a session handoff triggersuch as a degradation in quality of communications through the firstleg. In response to this or another session handoff trigger, mobilestation 28 or mobility application 26 may use the park feature to parkthe call. For example, mobile station 28 may park the second call legwith call manager 24. As another example, mobile station 28 may requestthat mobility application 26 park the second call leg. This action maybe called the park operation. Note that the first call leg may bedropped at any appropriate time. However, according to particularembodiments, the fist call leg is maintained as long as the call has notbeen parked. Furthermore, according to particular embodiments, the firstcall leg may be maintained until a new call leg is created.

Mobile station 28 and/or mobility application 26 may utilize basestation 18 to create a new call leg through cellular network 12 to callmanager 24 or mobility application 26. For example, mobile station 28may dial a telephone number associated with mobility application 26. Asanother example, mobility application 26 may dial a telephone numberassociated with mobile station 28. After creating the new call leg, thepark feature may then be used to couple the new call leg to the parkedcall. In other words, the new call leg may be coupled to the second callleg to allow mobile station 28 to resume communications with the remotedevice. This action may be called the park retrieval operation.

In some embodiments, anchoring a communication session in enterprisenetwork 14 may provide for control of the communication session duringhandoff. Anchoring a communication session in enterprise network 14represents routing signaling through enterprise network 14. Whensignaling and data flow to mobile station 28 through base station 18,anchoring the communication session in enterprise network 14 may beparticularly useful, since enterprise network 14 might otherwise beexcluded from the signaling path. If enterprise network 14 is excludedfrom the signaling path, mobility application 26 and call manager 24cannot process handoff of the communication session.

Various methods may be used to anchor a communication session inenterprise network 14. Calls placed to mobile station 28 may be anchoredin enterprise network 14. For example, cellular network 12 may beprovisioned to route calls directed to the telephone number of mobilestation 28 to enterprise network 14. Furthermore, mobility application26 may control the cellular number associated with mobile station 28.Mobility application 26 may indicate to cellular network 12 when mobilestation 28 is registered with enterprise network 14 so that when callsare made to the telephone number, cellular network 12 will obtain ahandoff number associated with enterprise network 14 from mobilityapplication 26. In addition, a separate enterprise telephone number maybe associated with mobile station 28 so that calls to the separateenterprise telephone number will route through enterprise network 14,which can extend the call to mobile station 28 through cellular network12.

After receiving a telephone call intended for mobile station 28, callmanager 24 and/or mobility application 26 may include itself in asignaling path associated with the resulting communication session,whether the signaling path proceeds through cellular network 12 orenterprise network 14. Note that when a remote device exists outsideenterprise network 14, for example on cellular network 12, and mobilestation 28 is outside of a coverage area of access point 20, hairpinning media through gateway 22 may be appropriate. That is, mediacommunicated to gateway 22 from the remote device may be routed tomobile station 28 without requiring the media to pass through enterprisenetwork 14. Similarly, media communicated to gateway 22 from mobilestation 28 may be routed to the remote device without requiring themedia to pass through enterprise network 14.

Calls placed by mobile station 28 may be anchored in enterprise network14 by first seeking to utilize enterprise network 14 when a user ofmobile station 28 dials a telephone number. To the extent mobile station28 is in an area serviced by access point 20, any communication sessionmay be anchored in enterprise network 14 by utilizing access point 20.When mobile station 28 is located outside the area serviced by accesspoint 20, mobile station 28 may first couple to mobility application 26through cellular network 12. For example, cellular network 12 may beprovisioned to redirect calls into enterprise network 14. Mobilityapplication 26 may then couple mobile station 28 to the intended remotedevice by dialing the phone number on behalf of mobile station 28.Alternatively or in addition, mobile station 28 may dial an IVR serviceprovided by enterprise network 14. A user of mobile station 28 may thenuse the IVR service to dial the target number.

Anchoring a call in enterprise network 14 may allow mobile station 28alone or in combination with mobility application 26 to invoke PBXfeatures within enterprise network 14, such as PBX features controlledby call manager 24, to effect handoff between enterprise network 14 andcellular network 12. For example, consider the case in which a caller inPSTN 16 calls mobile station 28 while mobile station 28 is an areaserviced by base station 18. In this case, if the phone number of mobilestation 28 is associated with enterprise network 14, call signalingtravels through PSTN 16 and enters enterprise network 14 through gateway22. Gateway 22, alone or in combination with call manager 24 and/ormobility application 26, extends the call back through PSTN 16 andcellular network 12 to mobile station 28. Using appropriatecommunications, mobile station 28 or mobility application 26 may invokea PBX feature when appropriate to effect handoff from cellular network12 to enterprise network 14. For example, if mobile station 28 enters oris located in an area serviced by access point 20, and mobile station 28desires to utilize enterprise network 14, steps may be taken to effecthandoff from cellular network 12 to enterprise network 14 using a PBXfeature hosted by enterprise network 14. According to a particularembodiment, dial tone multi-frequency (DTMF) signals may be communicatedto mobility application 26 or call manager 24 to invoke a PBX feature.

Note that communication system 10 represents one embodiment of a systemthat supports handoff between cellular and enterprise wireless networks.Various alternative embodiments are possible. For example, while in theillustrated embodiment enterprise network 14 couples to cellular network12 through PSTN 16 using gateway 22, various other embodiments mayinclude enterprise network 14 coupling to cellular network 12 in otherways. For example, enterprise network 14 may couple to cellular network12 using a service provider that supports VoIP. Thus, in alternativeembodiments, cellular network 12 and gateway 22 may not be included incommunication system 10.

FIG. 2 is a block diagram illustrating functional components of mobilityapplication 26. In the embodiment illustrated, mobility application 26includes call manager 24, as well as a processor 40, a network interface42, and a memory 44. These functional elements can operate to supporthandoff of active communication sessions when mobile station 28 roamsbetween cellular network 12 and enterprise network 14.

Processor 40 controls the operation and administration of elementswithin mobility application 26. For example, processor 40 operates toprocess information received from network interface 42 and memory 44.Processor 40 includes any hardware and/or logic elements operable tocontrol and process information. For example, processor 40 may be aprogrammable logic device, a microcontroller, and/or any other suitableprocessing device.

Network interface 42 communicates information to and receivesinformation from devices coupled to enterprise network 14. For example,network interface 42 may communicate with gateway 22, call manager 24,and access point 20. Furthermore, network interface 42 may receiveinformation from and transmit information to remote devices as well asmobile station 28. Thus, network interface 42 includes any suitablehardware or controlling logic used to communicate information to or fromelements coupled to mobility application 26.

Memory 44 stores, either permanently or temporarily, data and otherinformation for processing by processor 40 and communication usingnetwork interface 42. Memory 44 includes any one or a combination ofvolatile or nonvolatile local or remote devices suitable for storinginformation. For example, memory 44 may include random access memory(RAM), read only memory (ROM), magnetic storage devices, optical storagedevices, or any other suitable information storage device or acombination of these devices. As illustrated, memory 44 may include oneor more memory modules, such as code 46 and handoff numbers 48.

Code 46 includes software, executable files, and/or appropriate logicmodules capable when executed to control the operation of mobilityapplication 26. For example, code 46 may include executable filescapable of supporting handoff between cellular network 12 and enterprisenetwork 14. Code 46 may include instructions to enable mobilityapplication 26 to utilize PBX features to redirect incoming call legs toparked communication sessions. Handoff numbers 48 include E.164telephone numbers that mobility application 26 may use and/or provide tomobile station 28 for use in effecting handoff between cellular network12 and enterprise network 14. For example, mobility application 26 maybe assigned static E.164 numbers for handoff purposes.

In operation, network interface 42 may receive an indication from mobilestation 28 that mobile station 28 intends to utilize a second network,for example cellular network 12. In some embodiments, processor 40 maycommunicate a handoff number selected from handoff numbers 48 to mobilestation 28 through network interface 42.

Note that mobility application 26 may utilize session descriptionprotocol (SDP) to bridge media. Use of SDP may provide for more securehandoff by associating incoming legs with parked legs only when SDPidentifiers match. Furthermore, mobility application may use anyappropriate protocol to communicate with other elements of system 10.For example, mobility application 26 may utilize Java telephonyapplication programming interface (JTAPI) to interact with call manager24.

While this example includes specific functional components for mobilityapplication 26, mobility application 26 may include any collection andarrangement of components, including some or all of the enumeratedfunctional components, for supporting handoff between cellular network12 and enterprise network 14. Moreover, mobility application 26contemplates implementing each of the functional components using anysuitable combination and arrangement of hardware and/or logic, andimplementing any of the functionalities using a computer program storedon a computer-readable medium. Furthermore, mobility application 26 maybe implemented as a stand-alone device, or aspects of mobilityapplication 26 may be distributed among various devices withinenterprise network 14. Alternatively, in some embodiments mobilityapplication 26 may be incorporated into call manager 24.

FIG. 3 is a block diagram illustrating functional components of mobilestation 28. In the embodiment illustrated, mobile station 28 includes auser interface 60, a controller 62, a cellular interface 64, anenterprise interface 66, and a memory 68. In general, mobile station 28may establish communication sessions with remote devices throughinteraction with cellular network 12 and/or enterprise network 14.Moreover, mobile station 28 may effect handoff between cellular network12 and enterprise network 14.

User interface 60 allows a user of mobile station 28 to inputinformation into mobile station 28 and receive information outputted bymobile station 28. For example, user interface 60 may receive audioinformation from a user of mobile station 28. User interface 60 may alsoallow the user to dial telephone numbers and select from variousfeatures made available by mobile station 28. In addition, audioinformation may be outputted by user interface 60 to the user. Thus,user interface 60 may include a microphone, speaker, keypad, and/orother appropriate devices for inputting and outputting information.

Controller 62 controls the operation and administration of the elementswithin mobile station 28. For example, controller 62 operates to processinformation and/or commands received from user interface 60, cellularinterface 64, enterprise interface 66, and memory 68. Controller 62includes any hardware and/or logic elements operable to control andprocess information. For example, controller 62 may be amicrocontroller, processor, programmable logic device, and/or any othersuitable processing device.

Cellular interface 64 communicates information to and receivesinformation from cellular network 12. For example, cellular interface 64may communicate and receive audio information and signaling dataassociated with telephone calls placed through cellular network 12.Thus, cellular interface 64 includes any suitable hardware orcontrolling logic used to communicate information to or from elementscoupled to mobile station 28.

Enterprise interface 66 communicates information to and receivesinformation from enterprise network 14. For example, enterpriseinterface 66 may communicate and receive audio information and signalingdata associated with telephone calls placed through enterprise network14. Thus, enterprise interface 66 includes any suitable hardware orcontrolling logic used to communicate information to or from elementscoupled to mobile station 28.

Note that, as illustrated, mobile station 28 includes multiple antennas.Use of multiple antennas may allow mobile station 28 to simultaneouslycouple to multiple wireless networks. For example, a first antennacouple to cellular interface 64 to provide for communication withcellular network 12, while a second antenna may couple to enterpriseinterface 66 to provide for communication with enterprise network 14.However, mobile station 28 may include any number of antennas, includingone antenna, to provide for simultaneous and/or serial communicationswith various networks.

Memory 68 stores, either permanently or temporarily, data and otherinformation for processing by controller 62 and communication using userinterface 60, cellular interface 64, and/or enterprise interface 68.Memory 68 includes any one or a combination of volatile or nonvolatiledevices suitable for storing information. For example, memory 68 mayinclude RAM, ROM, magnetic storage devices, optical storage devices, orany other suitable information storage device or a combination of thesedevices. As illustrated, memory 68 may include one or more memorymodules, such as code 70, handoff numbers 72, and session handoffthresholds 74.

Code 70 includes software, executable files, and/or appropriate logicmodules capable when executed to control the operation of mobile station28. For example, code 70 may include executable files capable ofeffecting handoff between cellular network 12 and enterprise network 14.Code 70 may include instructions to enable mobile station 28 to placestealth calls to create new call legs for handoff purposes. Code 70 mayalso include instruction to enable mobile station 28 to utilize PBXfeatures such as park to handoff communication sessions from one networkto another. Handoff numbers 72 include E.164 telephone numbers thatmobile station 28 may use to effect handoff between cellular network 12and enterprise network 14. For example, mobile station 28 may dial E.164numbers to place stealth calls. Session handoff thresholds 74 includedata, such as acceptable and unacceptable error rates associated withcommunication sessions. Session handoff thresholds 74 may be used bymobile station 28 to determine when to seek handoff between cellularnetwork 12 and enterprise network 14. More specifically, session handoffthresholds 74 may specify thresholds for use when mobile station 28 hasan active communication session.

In operation, controller 62 may maintain registration with call manager24 when mobile station 28 is located within an area serviced by accesspoint 20. Controller 62 may operate to communicate voice data receivedthrough user interface 60 as well as signaling data through base station18 and/or access point 20 to cellular network 12 and/or enterprisenetwork 14. Controller 62 may also operate to communicate voice datareceived through cellular interface 64 and/or enterprise interface 66 toa user of mobile station 28 through user interface 60. In addition,controller 62 may use session handoff thresholds 74 to determine when toeffect handoff between cellular network 12 and enterprise network 14.For example, controller 62 may determine that an session handoffthreshold 74 associated with communication session using enterpriseinterface 66 has been exceeded, and controller 62 may register withcellular network 12 using cellular interface 64 and place a stealth callthrough cellular network 12 to mobility application 26 using a handoffnumber 72. Furthermore, controller 62 may communicate commands to callmanager 24 and/or mobility application 26 through cellular interface 64and/or enterprise interface 66 to utilize PBX features for handoffpurposes.

While this example includes specific functional components for mobilestation 28, mobile station 28 may include any collection and arrangementof components, including some or all of the enumerated functionalcomponents, for communicating with remote devices using cellular network12 and/or enterprise network 14 and effecting handoff between cellularnetwork 12 and enterprise network 14 using PBX features. Moreover,mobile station 28 contemplates implementing each of the functionalcomponents using any suitable combination and arrangement of hardwareand/or logic. Thus, in one embodiment mobile station 28 is a mobilephone. In other embodiments, mobile station 28 may be a personal digitalassistant (PDA), laptop computer, or other device operable to establishcommunications with cellular network 12 and enterprise network 14.

Prior to discussing FIG. 4, the problems or situations that are beingaddressed by the proposed flows should be understood. Consider anoperation of an example embodiment, where a call associated with mobilestation 28 is being properly anchored by mobility application 26. Inorder to execute a handoff, a new cellular call must be made. Hence,mobile station 28 will make the cellular call over cellular network 12and to mobility application 26, whereby a switch occurs over to thatcall leg. Mobility application 26 is handling multiple calls andmultiple mobile stations. Hence, mobility application 26 needs toassociate that particular call to a given mobile station, particularlyin the context of handoff scenarios. A significant obstacle is presentin trying to associate a first call (e.g. a cellular call) and a secondcall (e.g. a VoIP call). This challenge is successfully overcome by theteachings of the present invention, as evidenced by FIG. 4, which isdetailed below.

FIG. 4 illustrates several methods for addressing the situation where anincoming cellular call is coming in from mobility application 26 and thecall needs to be associated with the existing VoIP call. One way is touse a park code, which is illustrated in the flowchart by steps 102-126.

The park scenario of FIG. 4 illustrates another method 100 for effectinghandoff between cellular network 12 and enterprise network 14. Mobilestation 28 establishes a communication session with a remote deviceusing enterprise network 14 at step 102. Note that in some embodimentsmobile station 28 maintains registration with call manager 24 and/ormobility application 26 while mobile station 28 remains within range ofaccess point 20. Thus, call manager 24 may direct incoming callsintended for mobile station 28 through access point 20 when mobilestation 28 is registered, and direct incoming calls intended for mobilestation 28 through PSTN 16 when mobile station 28 is not registered.Similarly, a user of mobile station 28 may dial a telephone number andmobile station 28 may communicate signaling information through accesspoint 20 to enterprise network 14 and call manager 24 when mobilestation 28 has registered with call manager 24. Note that the remotedevice associated with the communication session may be located inenterprise network 14 or outside enterprise network 14, such as in PSTN16 or cellular network 12.

Mobile station 28 may detect eminent loss of signal on the enterprisenetwork 14 at step 104. For example, as discussed above, mobile station28 may monitor data associated with enterprise network 14 and comparethe data with session handoff thresholds 74. Mobile station 28 invokesundirected park at step 106. Undirected park may be invoked by a user ofmobile station 28 or automatically by mobile station 28. Mobile station28 receives a park number from call manager 24 at step 108. At step 110,mobile station 28 determines whether the received park number is in anE.164 range. If the received park number is an E.164 range, mobilestation 28 registers with cellular network 12 at step 112 and dials thepark number at step 114. At step 116, mobile station 28 is reconnectedto the parked communication session.

Returning to step 110, if the received park number is not in an E.164range, mobile station 28 communicates the park number to mobilityapplication 26 at step 118. At step 120, mobile station 28 receives ahandoff number from mobility application 26. The handoff number receivedmay be a dialable number in an E.164 range so that mobile station 28 mayuse the handoff number to couple to mobility application 26 throughcellular network 12. Thus, mobile station 28 registers with the cellularnetwork 12 at step 122 and dials the handoff number at step 124. At step126, mobility application 26 dials the park number on behalf of mobilestation 28. At step 116, mobile station 28 is reconnected to the parkedcommunication session.

In some embodiments, a media break may occur during handoff. However,audio notifications associated with the handoff, such as music on hold,ringing, and other indications and sounds may be suppressed by mobilestation 28. Alternatively or in addition, mobile station 28 maycommunicate information to a user of mobile station 28 that a handoff isoccurring. Furthermore, note that method 100 might involve parking thecommunication session before placing the stealth call. However, in someembodiments, mobile station 28 may place a stealth call before parkingthe communication session, and only park the communication session afterdetecting answer by mobility application 26. Using this sequence, thelength of the media break may be reduced or eliminated.

Note that method 100 utilizes undirected park. Alternatively or inaddition, directed park may be utilized. Using directed park, mobilestation 28 may determine available park numbers and select one of theavailable park numbers for use in handoff. In some embodiments, mobilestation 28 and/or particular communication sessions may be assignedspecific park numbers to use when appropriate. Furthermore, mobilestation 28 may be able to monitor what park numbers are being used atany time. If the selected park number is an E.164 number, when mobilestation 28 determines to utilize cellular network 12, mobile station 28may dial the park number directly. If the park number is not an E.164number, mobile station 28 may register the park number with mobilityapplication 26, and mobility application 26 may map the park number toan E.164 number for park retrieval.

Method 100 illustrates handoff from enterprise network 14 to cellularnetwork 12. However, handoff from cellular network 12 to enterprisenetwork 14 may occur using similar techniques. In some embodiments,handoff from cellular network 12 to enterprise network 14 may includeuse of DTMF signals communicated from mobile station 28 to cellularnetwork 12 being converted into a feature indication when mobile station28 enters an area serviced by access point 20. To utilize DTMF signalsto invoke PBX features, communication sessions may be required to anchorin enterprise network 14. After anchoring a communication in enterprisenetwork 14, when mobile station 28 determines that enterprise network 14may be available, mobile station 28 may provide a sequence of DTMFsignals corresponding to a feature activation code. When the DTMFsignals traveling through cellular network 14 enter enterprise network14, the DTMF signals may be converted into a feature activator in orderto park the communication session. In the undirected park embodiment, apark number may be communicated via DTMF signals to mobile station 28.In the directed park embodiment, the park number may be provided alongwith the feature activation code. Mobile station 28 may couple to theparked communication session through a new call leg established throughaccess point 20.

To provide for increased security, park retrievals may be required to bevalidated before allowing an incoming call leg to be coupled to a parkedcommunication session. For example, an identifier of a calling party maybe required to be matched to an identifier of the parking party.Furthermore, utilizing a method including mobility application 26 mayallow mobility application 26 to perform a security function withoutaltering a native park feature in call manager 24.

There are three other cases that can achieve the function of properlyassociating call legs. The three processes are permutations oralternatives of the first process outlined above, but differ in a numberof aspects as described in the following discussion. The three processesoutlined are identified with number designations: 1, 2, and 3, as isillustrated in FIG. 4. Each of the processes may share the first twosteps (step 102 and 104) of the preceding discussion associated with thepark feature. The first process (1) relates to using a unique handoffnumber. This allows for a determination of which active session shouldbe bound to the incoming call. This is because it can be recognized towhich number the incoming call is addressed. Thus, a pool of phonenumbers exist and when the incoming cellular call is received, it can beproperly matched. Recall that the task is to match the incoming cellularcall with an existing VoIP call. Hence, a phone number can bedynamically or statically associated with the VoIP call leg. This isidentified by step 130, where a unique handoff number is received. Atstep 132, the unique handoff number is communicated and then properlyreceived at step 134. At step 135, the unique handoff number is dialed.At step 136, mobility application 26 would then use the handoff numberto handoff the cellular call to the VoIP leg.

Turning to the second process (2), the second process is associated withusing a unique session ID. The second process begins at steep 138(subsequent to step 104), where a common handoff number and uniquesession ID are received. At step 140, the common handoff number andunique session ID are communicated and then suitably received frommobility application 26 at step 144. At step 145, the common handoffnumber is dialed. At step 146, the session ID is dialed, for example,using a DTMF code. At step 148, mobility application 26 then performs aneffective handoff.

The third process (3) is associated with a caller ID scenario. The thirdprocess similarly picks up from step 104 and then moves to step 150,where the unique handoff number is then communicated. At step 152, thecommon handoff number is communicated and the common handoff number isthen received from mobility application at 154. At step 156,registration with the cellular network occurs and the handoff number isthen dialed in step 158. Following these operations, and at step 160,mobility application 26 uses the caller ID or ANI to associate thecellular call with the VoIP call. A proper handoff is then executed instep 162.

The preceding flowcharts illustrate particular methods for effectinghandoff between cellular network 12 and enterprise network 14. However,these flowcharts illustrate only exemplary methods of operation. Whilediscussion sometimes focuses on handoff in the enterprise-to-cellulardirection, similar techniques may be used to provide for handoff in thecellular-to-enterprise direction. Furthermore, communication system 10contemplates devices using any suitable techniques, elements, andapplications for performing these functions. Thus, many of the steps inthe flowcharts may take place simultaneously and/or in different ordersthan as shown. In addition, the devices may use methods with additionalsteps or fewer steps, so long as the methods remain appropriate.Moreover, other devices of system 10 may perform similar techniques tosupport handoff between cellular network 12 and enterprise network 14.

It is critical to note that the stages and steps in FIG. 4 illustrateonly some of the possible scenarios and operations that may be executedby, or within, the present system. Some of these stages and/or steps maybe deleted or removed where appropriate, or these stages and/or stepsmay be modified, enhanced, or changed considerably without departingfrom the scope of the present invention. In addition, a number of theseoperations have been described as being executed concurrently with, orin parallel to, one or more additional operations. However, the timingof these operations may be altered. The preceding example flows havebeen offered for purposes of teaching and discussion. Substantialflexibility is provided by the tendered architecture in that anysuitable arrangements, chronologies, configurations, and timingmechanisms may be provided without departing from the broad scope of thepresent invention. Accordingly, communications capabilities, dataprocessing features and elements, suitable infrastructure, and any otherappropriate software, hardware, or data storage objects may be includedwithin communication system 10 to effectuate the tasks and operations ofthe elements and activities associated with executing handoff functions.

Although the present invention has been described in detail withreference to particular embodiments, it should be understood thatvarious other changes, substitutions, and alterations may be made heretowithout departing from the spirit and scope of the present invention.The illustrated network architecture of FIG. 1 has only been offered forpurposes of example and teaching. Suitable alternatives andsubstitutions are envisioned and contemplated by the present invention:such alternatives and substitutions being clearly within the broad scopeof communication system 10. For example, the use of gateway 22 could besupplanted by bridges, switches, routers or any other suitable devicesthat are conducive to network communications. In addition the use ofDTMF is only one example signaling protocol. DTMF can be supplanted withSMS or any other signaling channel that is available in the cellular orPSTN network.

Numerous other changes, substitutions, variations, alterations, andmodifications may be ascertained to one skilled in the art and it isintended that the present invention encompass all such changes,substitutions, variations, alterations, and modifications as fallingwithin the spirit and scope of the appended claims.

1. A method comprising: anchoring a call for a mobile station in an enterprise network; invoking a private branch exchange (PBX) park feature for parking the call in order to facilitate a handoff of the call to a cellular network, the park feature hosted by the enterprise network; receiving from the enterprise network a park number for the park feature; determining whether the park number is within range; if the park number is within range, calling the park number to reconnect to the parked call; and if the park number is not within range: sending the park number to the enterprise network to obtain a handoff number; and registering with the cellular network to call the handoff number in order to initiate calling of the park number to reconnect to the parked call.
 2. The method of claim 1: the call comprising a first call leg and a second call leg, the first call leg between the mobile station and the enterprise network, the second call leg between the enterprise network and a remote device; and the invoking the park feature for parking the call further comprising: the invoking the park feature to park the second call leg.
 3. The method of claim 1: the call comprising a first call leg and a second call leg, the first call leg between the mobile station and the enterprise network, the second call leg between the enterprise network and a remote device; and further comprising: initiating creation of a third call leg between the cellular network and the enterprise network; and utilizing the park feature to couple the third call leg to the second call leg.
 4. The method of claim 1, the registering with the cellular network to call the handoff number in order to initiate calling of the park number further comprising: calling of the park number by a mobility application on behalf of the mobile station.
 5. The method of claim 1, the invoking the park feature for parking the call further comprising: invoking the park feature in response to detecting eminent loss of signal.
 6. The method of claim 1, the invoking the park feature for parking the call further comprising: sending one or more dial tone multi-frequency (DTMF) signals to invoke the park feature.
 7. The method of claim 1, the determining whether the park number is within range further comprising: determining whether the park number is within an E.164 range.
 8. An apparatus comprising: a memory configured to store code; and a processor configured to execute the code to: anchor a call for a mobile station in an enterprise network; invoke a private branch exchange (PBX) park feature for parking the call in order to facilitate a handoff of the call to a cellular network, the park feature hosted by the enterprise network; receive from the enterprise network a park number for the park feature; determine whether the park number is within range; if the park number is within range, call the park number to reconnect to the parked call; and if the park number is not within range: send the park number to the enterprise network to obtain a handoff number; and register with the cellular network to call the handoff number in order to initiate calling of the park number to reconnect to the parked call.
 9. The apparatus of claim 8: the call comprising a first call leg and a second call leg, the first call leg between the mobile station and the enterprise network, the second call leg between the enterprise network and a remote device; and the processor further configured to invoke the park feature for parking the call by: the invoking the park feature to park the second call leg.
 10. The apparatus of claim 8: the call comprising a first call leg and a second call leg, the first call leg between the mobile station and the enterprise network, the second call leg between the enterprise network and a remote device; and the processor further configured to: initiate creation of a third call leg between the cellular network and the enterprise network; and utilize the park feature to couple the third call leg to the second call leg.
 11. The apparatus of claim 8, the processor further configured to register with the cellular network to call the handoff number in order to initiate calling of the park number by: calling of the park number by a mobility application on behalf of the mobile station.
 12. The apparatus of claim 8, the processor further configured to invoke the park feature for parking the call by: invoking the park feature in response to detecting eminent loss of signal.
 13. The apparatus of claim 8, the processor further configured to invoke the park feature for parking the call by: sending one or more dial tone multi-frequency (DTMF) signals to invoke the park feature.
 14. The apparatus of claim 8, the processor further configured to determine whether the park number is within range by: determining whether the park number is within an E.164 range. 